Performance evaluation of a porous polymer-nickel foam compound cooler combining radiative and evaporative cooling

The radiative cooling technology and evaporative cooling technology have drawn intense attentions due to zero energy consumption and negligible carbon footprint, and the afflatus to combine the above two passive cooling technologies has been strongly inspired. The compound cooling mode combining radiative cooling and evaporative cooling can theoretically break through the application limitations under the harsh environmental conditions, but the specific cooling performance needs to be further investigated in conjunction with actual environmental conditions. Herein, a porous polymer-nickel foam (PP-NF) compound cooler is fabricated. The upper porous polymer radiative coating (PPRC) is the radiative cooling layer, and the emissivity is as high as 97% within the atmospheric window (8–13 μm), while the reflectivity is about 98% and 94% in the visible wavelength range (0.38–0.78 μm) and the solar spectrum wavelength range (0.25–2.5 μm), demonstrating remarkable radiative cooling capability. The bottom nickel foam filled with anhydrous calcium chloride (CaCl2) is the evaporative cooling layer, which can absorb water in nighttime to meet the needs of efficient evaporative cooling in daytime. The comprehensive properties of the PP-NF cooler are very impressive for cooling applications, and the outdoor experimental and theoretical results show that the temperature drop and cooling power of the PP-NF cooler can reach 2.7 °C (12:00–13:00) and 100.30 W/m2 (12:00–16:00), which are increased by 42.1% and 24.7% compared to the PPRC cooler with radiative cooling only. Furthermore, the cooling performance of the PP-NF cooler is better than the evaporative cooler in high humidity environment with the relative ambient humidity exceeding 63% through the quantitative analysis of experimental and related theoretical results. The PP-NF cooler has a bright application prospect, and it is very likely to play an indispensable role in the improvement and optimization of the energy framework in the foreseeable future.